1. Field of the Invention
The present invention relates generally to medical devices, and in particular, to core wires used in catheters and the like.
2. Description of the Related Art
Medical catheters, such as guidewires and balloon catheters, have been proven efficacious in treating a wide variety of blood vessel disorders. Moreover, these types of catheters have permitted clinicians to treat disorders with minimally invasive procedures that, in the past, would have required complex and perhaps life threatening surgeries. For example, balloon angioplasty is now a common procedure to alleviate stenotic lesions (i.e., clogged arteries) in blood vessels, thereby reducing the need for heart bypass operations.
Because medical catheters must be passed through a tortuous blood vessel network to reach the intended treatment site, it is desirable that the catheters be fairly flexible, especially at the distal end. However, the distal end must not be so flexible that it tends to bend back upon itself when the clinician advances the catheter distal end through the patient.
One method of imparting desired flexibility characteristics to a catheter has been to incorporate a xe2x80x9ccore wirexe2x80x9d into the distal end of the catheter. A core wire is a wire that extends from the distal end of a catheter body, providing structural support to the distal end to prevent bend backs or kinks during catheter advancement. Furthermore, the core wire is also flexible, such that the catheter distal end may navigate tortuous blood vessel networks or other body cavities.
Previously known catheter core wires are of complex construction, requiring multiple manufacturing steps to incorporate the core wire into the catheter. This increases manufacturing costs of the catheter, which ultimately are passed on to hospitals and patients. Moreover, previously known core wires may not be sufficiently flexible. Accordingly, there exists a need for catheter core wires that are easier to manufacture, and which possess the desired flexibility profiles.
Previously known catheter core wires also may not be sufficiently rigid at the very distal tip of the wire. In particular, catheter core wires are commonly formed of superelastic materials such as NiTi alloys which exhibit an elastic response when subject to stress. Superelasticity refers to the ability of a material to undergo deformation and to return to its original configuration without being permanently or xe2x80x9cplasticallyxe2x80x9d deformed. This superelasticity, often referred to as transformational superelasticity, exhibits itself as the parent crystal structure of the material as it transforms into a different crystal structure. In superelastic materials the parent crystal structure is known as the austenitic phase and the product crystal structure is known as the martensitic phase. Such formed martensite is termed stress-induced martensite.
While superelasticity may be desirable for the majority of the core wire, superelasticity at the very distal tip of the core wire creates the problem that the tip will not be shapeable. Shapeability is desirable so that a doctor or other person inserting the catheter into the body can shape the tip into a form advantageous for insertion and navigation through the body. If the tip of the core wire is superelastic, the material cannot be shaped.
An additional problem with previously known core wires is that they may not be securely attached to the distal end of the catheter. What is needed is a method to make the connection between the catheter and the core wire secure so that the stress of vascular navigation will not cause breakages.
The present invention addresses the needs raised above by providing a catheter core wire with improved flexibility and a simple and easily manufacturable design. In one aspect of the present invention, there is provided a catheter with a tubular body having a proximal end and a distal end. The tubular body has a lumen extending therethrough. An expandable member is mounted on the distal end of the tubular body. The expandable member has a proximal portion and a distal portion which are both mounted to the tubular body.
A core wire is inserted into the lumen at the distal end. The core wire has an end mounted within the lumen and an extending portion which extends from the distal end of the tubular body. The extending portion is tapered through a length of no more than 60 mm but at least 5 mm, preferably 60 to 15 mm, more preferably 50 to 15 mm, and optionally 35 to 15 mm.
In one aspect of the present invention, the core wire is tapered over a length of no more than 40 mm but at least 10 mm, and is made of a nitinol alloy or stainless steel. The core wire may have a first cross-sectional area at one end of the taper and a second cross-sectional area at the other end of the taper, the first cross-sectional area being greater than the second cross-sectional area by at least 20%. In another embodiment, the first cross-sectional area is greater than the second cross-sectional area by at least 70%. In these embodiments, the extending portion may also have a region of constant cross-sectional area.
In another aspect of the present invention, there is provided a hollow guidewire formed from a hypotube having a proximal end and a distal end. The proximal end has a first wall thickness and the distal end has a second wall thickness. The first wall thickness is greater than the second wall thickness. An expandable member is mounted on the distal end of the hypotube, and there is a tapered core wire extending from the distal end of the hypotube. In one embodiment, the hypotube is made of nitinol, and the first wall thickness is 20% greater than the second wall thickness.
In another aspect of the present invention, there is provided a hollow guidewire, formed of a nitinol hypotube having a proximal end and a distal end. The nitinol hypotube has a lumen extending between the proximal and distal ends. An expandable member is mounted on the distal end. A core wire is inserted into the lumen at the distal end of the nitinol hypotube, and the distal end is crimped on the core wire to secure it within the lumen.
In another aspect of the present invention, there is provided a catheter having a tubular body. The tubular body has a proximal end and a distal end, and an irrigation lumen extending therethrough. An irrigation opening is on the distal end of the tubular body. The irrigation opening is in fluid communication with the irrigation lumen. A core wire has an end mounted within the lumen. The core wire has an extending portion which extends from the distal end of the tubular body, the extending portion being tapered through a length of no more than 60 mm but at least 5 mm.
In another aspect of the present invention, there is provided core wire with a shapeable tip and method of manufacturing the same. A core wire previously made superelastic is subject to additional processing to remove superelasticity from a distal tip, thereby allowing the material at the distal tip to be shapeable to aid in advancing the core wire through a blood vessel or other body cavities.
In one embodiment, the core wire is manufactured by first providing an elongate body of NiTi alloy or similar material. This elongate body is subject to a first cold working in the range of about 20 to 40%. A heat treatment in the range of about 300xc2x0 to 600xc2x0 C. for 10 seconds to 60 minutes is performed to impart superelasticity to the body. Following heat treatment, the distal end of the core wire is cold worked from about 10 to 50%, removing superelasticity from this end and producing a shapeable tip at the end of the core wire. The core wire that results is a flexible, superelastic body having a shapeable distal tip with no superelasticity.
Alternatively, once the NiTi is imparted with superelasticity, the distal end of the core wire can be removed of its superelasticity by an additional heat treatment. Heat treatments at temperatures of about 400-800xc2x0 C. for extended periods of time will cause the material to lose its superelasticity at the distal end. Additionally, superelasticity can be imparted to the core wire by a solution treatment followed by aging process.
In another embodiment of the present invention, a method is provided for securing the core wire to the distal end of an elongated catheter tubular body.
Conventional means for attaching a core wire to a catheter body is by soldering, which uses flux of hydrogen. NiTi alloys are susceptible to hydrogen embrittlement, which will in turn diminish the tensile strength of the material. Because of the stresses involved in advancing the catheter through a vessel network, it has been discovered that a core wire soldered to a catheter may break off during catheter advancement. In one aspect of the present method, the tubular body is mechanically crimped onto the core wire to secure the core wire in place. This crimping method has been found to increase the strength of the bond between the core wire and the catheter tube so that greater pull force is required to break the core wire off from the catheter.
In another aspect of the present invention, a medical catheter is provided comprising an elongate tubular body having a proximal end and a distal end and a lumen extending therethrough. An expandable member is mounted to the distal end of the tubular body. A core wire having a proximal taper and a distal taper extends from the distal end of the tubular body. In one preferred embodiment, the core wire has a section of substantially constant diameter between the proximal taper and distal taper that is crimped to the tubular body. The core wire preferably extends into the lumen at the distal end over a length of about 10 to 100 mm to provide additional structural support to the tubular body.
In another aspect of the present invention, a core wire is provided comprising an elongate body having a proximal end and a distal end and superelastic properties. A shapeable distal tip extends from the distal end of the elongate body. A proximally tapered transition section is provided between the distal end of the elongate body and the distal tip.